The term "superconductivity" is applied to the phenomenon of immeasurably low electrical resistance exhibited by materials. Until recently superconductivity had been reproducibly demonstrated only at temperatures near absolute zero. As a material capable of exhibiting superconductivity is cooled, a temperature is reached at which resistivity decreases (conductivity increases) markedly as a function of further decrease in temperature. This is referred to as the superconducting onset transition temperature or, in the context of superconductivity investigations, simply as the critical temperature (T.sub.c). T.sub.c provides a conveniently identified and generally accepted reference point for marking the onset of superconductivity and providing temperature rankings of superconductivity in differing materials. The highest temperature at which superconductivity is observed in a material is designated T.sub.o.
Unless otherwise indicated, the term "thick film" refers to films having thicknesses of greater than 5 .mu.m while the term "thin film" refers to films having thicknesses which are in all instances less than 5 .mu.m and more typically less than 1 .mu.m.
The following art is relevant or was previously cited by the Examiner in one or more patent applications previously filed claiming the subject matter of this invention:
P-1: J. G. Bednorz and K. A. Muller, "Possible High T.sub.c Superconductivity in the Ba-La-Cu-O System", Z. Phys. B.-Condensed Matter, Vol. 64, pp. 189-193 (1986) revealed that polycrystalline compositions of the formula Ba.sub.x La.sub.5-x Cu.sub.5 O.sub.5(3-y), where x=1 and 0.75 and y&gt;0 exhibited superconducting transition temperatures in the 30.degree. K. range.
P-2: C. W. Chu, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, and Y. Q. Wang, "Evidence for Superconductivity above 40K in the La-Ba-Cu-O Compound System", Physical Review Letters, Vol. 53, No. 4, pp. 405-407, January 1987, reported increasing T.sub.c to 40.2.degree. K. at a pressure of 13 kbar. At the end of this article it is stated that M. K. Wu increased T.sub.c to 42.degree. K. at ambient pressure by replacing Ba with Sr.
P-3: C. W. Chu, P. H. Hor, R. L. Meng, L. Gao, and Z. J. Huang, "Superconductivity at 52.5K in the Lanthanum-Barium-Copper-Oxide System", Science Reports, Vol. 235, pp. 567-569, January 1987, a T.sub.c of 52.5.degree. K. for (La.sub.0.9 Ba.sub.0.1).sub.2 CuO.sub.4-y at high pressures.
P-4: R. J. Cava, R. B. vanDover, B. Batlog, and E. A. Rietman, "Bulk Superconductivity at 36K in La.sub.1.8 Sr.sub.0.2 CuO.sub.4 ", Physical Review Letters, Vol. 58, No. 4, pp. 408-410, January 1987, reported resistivity and magnetic susceptibility measurements in La.sub.2-x Sr.sub.x CuO.sub.4, with a T.sub.c at 36.2.degree. K. when x=0.2.
P-5: J. M. Tarascon, L. H. Greene, W. R. McKinnon, G. W. Hull, and T. H. Geballe, "Superconductivity at 40K in the Oxygen-Defect Perovskites La.sub.2-x Sr.sub.x CuO.sub.4-y ", Science Reports, Vol. 235, pp. 1373-1376, Mar. 13, 1987, reported title compounds (0.05.ltoreq.x.ltoreq.1.1) with a maximum T.sub.c of 39.3.degree. K.
P-6: M. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, Y. Q. Wang, and C. W. Chu, "Superconductivity at 93K in a New Mixed-Phase Y-Ba-Cu-O Compound System at Ambient Pressure", Physical Review Letters, Vol. 58, No. 9, pp. 908-910, Mar. 2, 1987, reported stable and reproducible superconducting transition temperatures between 80.degree. and 93.degree. K. at ambient pressures for materials generically represented by the formula (L.sub.1-x M.sub.x).sub.a A.sub.b D.sub.y, where L=Y, M=Ba, A=Cu, D=O, x=0.4, a=2, b=1, and y.ltoreq.4.
P-7: Mir U.S. Pat. No. 4,880,770 discloses processes of preparing rare earth alkaline earth copper oxide thin films that are superconductive.
P-8: Kamioka et al Japanese 56-85814 Jul. 13, 1941, cited by the Examiner in U.S. Ser. No. 245,497, filed Sep. 18, 1988, now abandoned; discussed in U.S. Ser. No. 327,472, cited above.
P-10: Koinuma et al, "High T.sub.c Superconductivity in Screen Printed Yb-Ba-Cu-O Films", Jpn. J. of Appl. Phys., Vol. 26, No. 5, May 1987, pp. L761-762, cited by the Examiner in U.S. Ser. No. 245,497, cited above; discussed in U.S. Ser. No. 327,472, cited above.
P-11: Schmidberger et al U.S. Pat. No. 4,336,242, cited by the Examiner and discussed in U.S. Ser. Nos. 291,921 and 347,472, cited above.
P-12: Bianchi et al U.S. Pat. No. 4,395,436, cited by the Examiner and discussed in U.S. Ser. No. 347,472, cited above.
P-13: Suzuki et al U.S. Pat. No. 4,326,785, cited by the Examiner and discussed in U.S. Ser. No. 347,472, cited above.
P-14: T. Hashimoto, T. Kosaka, Y. Yoshida, K. Fueki, and H. Koinuma, "Superconductivity and Substrate Interaction of Screen-Printed Bi-Sr-Ca-Cu-O Films", Japanese Journal of Applied Physics, Vol. 27, No. 3, March, 1988, pp. L384-L386, reports successful attempts to form superconductive thick films of bismuth strontium calcium copper oxide on yttrium stabilized zirconia and strontium titanate substrates. Hashimoto et al failed to produce superconducting films on quartz and alumina substrates. The thick films were prepared by screen printing. Bismuth strontium calcium copper oxides with nominal 1112 and 2213 compositions were prepared by calcining bismuth and copper oxides with strontium and calcium carbonates for 800.degree. C. for 12 hours, followed by mixing with a mortar and pestle while adding octyl alcohol to form a paste. The paste was screen printed.
P-15: T. Nakamori, H. Abe, Y. Takahasi, T. Kanamori, and S. Shibata, "Preparation of Superconducting Bi-Ca-Sr-Cu-O Printed Thick Films Using a Coprecipitation of Oxalates", Japanese Journal of Applied Physics, Vol. 27, No. 4, April 1988, pp. L649-L651, reports successful attempts to form superconductive thick films of bismuth strontium calcium copper oxide on monocrystalline magnesia substrates. The thick films were prepared by screen printing. Calcium, strontium, and copper chlorides were coprecipitated with oxalates. Bismuth oxalate was separately precipitated from acetone. These two precipitates were separately washed, filtered, and dried before being mixed as solids and heated to 300.degree. C. Bismuth strontium calcium copper oxide with a nominal 1112 composition was prepared.
P-16: K. Hoshino, H. Takahara, and M. Fukutomi, "Preparation of Superconducting Bi-Sr-Ca-Cu-O Printed Thick Films on MgO Substrate and Ag Metal Tape", Japanese Journal of Applied Physics, Vol. 27, No. 7, July 1988, pp. L1297-L1299, reports successful attempts to form superconductive thick films of bismuth strontium calcium copper oxide on monocrystalline magnesia substrates, silver, and some metal tapes. The thick films were prepared by calcining techniques similar to those described by Hashimoto et al, cited above. The bismuth strontium calcium copper oxide exhibited a nominal 1112 composition.
P-17: Parker et al U.S. Pat. No. 4,571,350 cited by the Examiner and discussed in U.S. Ser. No. 291,921, cited above.
P-18: Kodas et al "Aerosol Flow Reactor Production of Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7 Powder: Fabrication of Superconducting Ceramics", Appl. Phys. Lett. 52(19) May 1988, pp. 1622-1624, cited by the Examiner and discussed in U.S. Ser. No. 291,921.
P-19: Nobumasa et al "Formation of a 100K Superconducting Bi(Pb)-Sr-Ca-Cu-O Film by Spray Prolysis", Japanese Journal of Applied Physics, Vol. 27, No. 9, September 2988, L1669-L1671, cited and discussed in U.S. Ser. No. 291,921, cited above.
P-20: Agostinelli et al U.S. Pat. No. 4,950,643, is directed to process of forming a heavy pnictide mixed alkaline earth copper oxide superconductive coating on a substrate by coating metal-organic ligand compounds on a substrate and converting the compounds to a crystalline electrical conductor by heating.